The present exemplary embodiment relates to an exhaust system for a motor vehicle, and particularly to a port receiving a sensor for measuring the amount of oxygen in an exhaust gas. It finds particular application in conjunction with an all-terrain vehicle (hereinafter referred to as “ATV”) and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other types of vehicles and applications.
The modern internal combustion engine of motor vehicles is equipped with an electronic control system which adjusts the quantity of fuel injected, the quantity of exhaust gas recirculated, etc., on the basis of preprogrammed strategies and as a function of engine operating conditions.
Among the items of information required by the electronic control system in order to determine the operating conditions include the composition and/or the temperature of the exhaust gases and more particularly to the residual oxygen concentration. These items of information relating to the exhaust gases are delivered by appropriate measuring sensors which are disposed along the path of the exhaust gases. These sensors often work according to the principle of an oxygen concentration chain. They normally consist of a pipe containing a solid electrolyte (e.g. ZrO2) which is acted upon by the exhaust gas on one side and by a gas with a known oxygen content on the other side.
Typically, the solid electrolyte requires a working temperature of about 400° to 900°, allowing the sensor to be screwed into the exhaust gas pipe through a port at a point where the exhaust gases have a temperature suitable to heat the probe to its working temperature. In a standard case, the measuring sensor with which the exhaust line is equipped is screwed into an internally threaded housing traversing the wall of the exhaust pipe, in such a way as to bring the analysis cells into contact with the flow of exhaust gases.
FIG. 1 shows a conventional gas sensor 1 of the type typically installed in an exhaust system of an automotive engine to control the air-fuel ratio. The gas sensor 1 includes a sensor element 2 inserted in a cylindrical housing 4, a measured gas cover 6 provided at a distal end side of the housing 4 to cover a distal end side of the sensor element 2, and an atmospheric air cover 8 provided at a proximal end side of the housing 4 to cover a proximal end side of the sensor element 2.
The inside space of the measured gas cover 6 includes a measured gas environment 7, while the inside space of the atmospheric air cover 8 includes an atmospheric air environment 10. The clearance between the sensor element 2 and the housing 4 should be sealed, to isolate environments 7 and 10 from each other. Furthermore, the clearance between the sensor element 2 and the housing 4 should be a watertight seal. Watertight sealing the clearance between the sensor element 2 and the housing 4 prevents fuel liquid from entering from the measured gas environment 7 and also prevents condensate from entering the measured gas environment 7 during an engine stopped condition.
Inorganic powder 12 fills the clearance between the sensor element 2 and the housing 4. An insulator 14 and a metallic ring 16 are disposed on the powder filler 12. The measured gas cover 6 includes an outer cover 18 and an inner cover 20. The atmospheric air cover 8 includes a main cover member 22 and an outside cover member 24. An atmospheric air side insulator 26 holds the lead wires 28 of the sensor element 2. The lead wires 28 are inserted in an elastic insulating member 30 provided at the proximal end side of the atmospheric air side insulator 26.
The oxygen concentration sensor is disposed in the exhaust pipe which conducts exhaust gas from the engine to a muffler. In the case of a saddle ride type all-terrain vehicle, for example, the engine exhaust pipe may be shielded to reduce heat transmitted to surrounding ATV components. This leads to a corresponding increase in the temperature of the exhaust gas downstream within the exhaust pipe. The oxygen concentration sensor has been found to experience a corresponding increase in temperature into a range that can affect performance.
The present disclosure introduces an oxygen sensor port including a boss design that has been found to advantageously reduce oxygen sensor temperature.